Hollow charge explosive device particularly for avalanche control

ABSTRACT

A shaped charge explosive device ( 10 ) comprising an explosive charge body including an explosive charge ( 18 ) defining a cavity particulate material ( 44 ) dispersible by the explosive charge when detonated, eg in a liner lining the cavity. In a preferred embodiment of this device of particular applicability to use in avalanche control, the particulate medium is aluminium. This is energized by the liner collapse and jetting process such that on impact and interaction with a snow/ice target it gererates a directed blast effect extending beyond that achievable with a simple blast charge of the same mass. Direct application to hand charge avalanche control methods and modified ammunition for Avalauncher ammunition are presented. Two of such charges with a conical liner can be positioned either facing each other or facing away form each other to obtain a particular blast pattern.

This application is a continuation in part of application Ser. No.09/412,764, Oct. 1, 1999 abandoned.

This invention relates to explosive devices commonly referred to ashollow charges or shaped charges. These essentially comprise a symmetricexplosive charge within which is formed a cavity lined by a liningmaterial. When the explosive charge is detonated the liner, of metal inknown devices, is subject to extremely high compressive loads which actto collapse and eject the liner material in the form of a high speedfluid jet, normally followed by a more slowly moving rigid slug. Thecharge and liner may be rotationally symmetric or non axi-symmetric, forexample with a liner with a “V” cross section, used for cuttingoperations.

There are a number of industrial applications for shaped charge deviceswhere rapid penetration effects are required in awkward and inaccessibleplaces. An example is to initiate or increase the yield of oil & gaswells. In this case a number of charges are arranged to fire radiallyoutwards at the base of the well. Upon detonation the shaped charge jetsperforate the steel well casing, surrounding concrete grouting and thenpenetrate deeply into the oil/gas bearing rock, producing a series ofdiscrete channels through which the oil and gas can flow into the wellconduit. Another application is perforation and clearance of refractorybung at the base of a steel smelting crucible. The most extensive use,however, is in the military context against heavily protected targetssuch as tanks and shelters and for a wide range of battlefieldengineering applications. In all these cases the shaped charges aredesigned and applied to exploit their penetration potential.

The present invention seeks to provide a shaped charge explosive deviceparticularly suitable for use for avalanche control. However, themechanism by which energy is distributed and imparted to the targetmedium by this invention offers potential for a number of alternativeapplications. The invention will be described in context with avalanchecontrol applications first, followed by alternative applications.

Avalanches can present a serious danger to people and property whentriggered in an uncontrolled manner, whether by a natural cause such asthe weather conditions or unintentionally as a result of human activitysuch as skiing or climbing. It has therefore become an establishedpractice in many mountainous areas to maintain a continuous programme ofavalanche control using explosives to trigger a release. This practiceof regularly triggering small controlled avalanches is intended tominimise the build up of snow in known start zones which, if left, wouldeventually release naturally and unexpectedly often cascading out ofcontrol. The current practices relevant to the present invention includethe following.

Where avalanche start zones are inaccessible, an explosive charge can bedelivered to the slope in the form of a projectile fired from a gun ormortar system where the projectile explodes on or shortly after impact.Short ranges (up to 3 km) can be covered by gas gun projector systemssuch as the nitrogen driven Avalauncher, used extensively in the US,Canada and Europe. Longer ranges demand high performance systems typicalof military artillery and the 105 mm howitzer and 106mm recoilless riflehave been used in avalanche control operations for many years.

Fuzes in older military ammunition are designed to detonate upon impact,in soft snow, however, these fuzes tend to trigger well below thesurface and quite probably not until the projectile strikes rock or firmground. In fact, the ideal point of burst for avalanche release isseveral meters above the surface in proximity mode. However, with gunfired projectiles, this can only be achieved with an electronicproximity burst fuze. Since this type of fuze is both inhibitivelyexpensive and notoriously unreliable against light, dispersed media suchas snow, the performance of impact fuzing continues to be tolerated.

Most areas in ski resorts are accessible, including the mountain peaks,and this accessibility enables explosive charges to be delivered orplaced by hand. The practice of positioning charges by hand is probablythe most cost effective and extensively used method of avalanche controlin many ski resorts, but carries with it obvious hazards in poor weatherconditions. The hand charge is a relatively simple device consisting ofa lightly cased (cardboard) explosive charge detonated by a length ofcapped pyrotechnic delay fuze. The fuze can be ignited and the chargethrown into a preferred position or the charge can be pre-positionedabove the surface on a bamboo stick before the fuze is ignited.

It is acknowledged that various types of anti-tank ammunition, bearingshaped charge liners, have been fired into avalanche start zones in thepast but this has been as a result of ammunition availability ratherthan an interest in the shaped charge effect. Results from this type ofordnance, designed specifically for high penetration into steel, hasnevertheless been no different from standard artillery fragmentingshells because little of the jet energy can be dissipated into the snowpack.

The present invention seeks to provide an improved hollow chargeexplosive device for this and other applications.

Accordingly, the present invention provides a hollow charge explosivedevice including an explosive charge defining boundary walls of a cavityand including particulate material located forward of said boundarywalls so as to be dispersible by said explosive charge when detonated.

The particulate material may be included in a liner lining the cavity orpositioned elsewhere forward of the cavity, eg in a nacelle, or in bothpositions.

The particulate material, if present in a liner, is driven in the sameway as that of a conventional shaped charge liner. However, in thiscase, the particulate medium forms into a highly energetic non-cohesivestream of particles, generally wider than that produced by aconventionally lined shaped charge. In this highly energised state, thelow bulk density of the liner material and high surface areaattributable to each particle of the liner material, together with thelarger surface area of the jets cross section, facilitates an intimateand violent kinetically stimulated reaction with the target medium.Given a knowledge of the intended target material and its constitution,eg a snow slab, the liner material can be chosen to optimise the blastenergy yield over and above that normally attributable to the explosivecharge alone.

Conveniently, the liner may comprise an inner liner skin and an outerliner skin defining a space therebetween and the particulate materialmay be a loose powder contained in that space. In a one embodiment, theinner liner skin and outer liner skin are of a glass reinforced plasticsmaterial. The particulate material may be aluminium powder, particularlyfor use in avalanche control due to the potentially highly reactivenature of aluminium powder with water.

In an alternative embodiment, the particulate material may be embeddedin an inert binder such as a plastics material, a was such as a paraffinwas, or an adhesive matrix to aid manufacture, handling and assembly.The matrix material may also be conveniently chosen to make a netcontribution to the reaction of the principal suspended particulatematerial.

Where a liner is not present, the high pressure and high temperaturegaseous stream produced by the hollow cavity in the explosive focusesblast effects only along the axis of the charge. If a particulatematerial is located on the axis of the charge, typically in the nacelle,this material will be energised and dispersed by the high pressure andhigh temperature gases ejected from the cavity, thereby furtherenhancing the directed blast effects produced by the hollow cavity.

An explosive device assembly may be formed from two such explosivedevices oriented such that the jets of liner formed on detonation of thecharges are directed towards each other or away from each other.

When the jets are directed toward each other, the collision of the jetswith each other provides an energetic response between the interactingjets. Two or more dissimilar liner materials may be provided in theexplosive devices which when brought together in collision with eachother and/or the target medium achieve an energetic response betweenassociated interacting materials. This effect may also be furtherenchanced with additional particulate material located in the nacelle.

The devices may be gun fired, or otherwise hand thrown, or form part ofa mechanically or chemically launched projectile.

An elongate support may be attached to the explosive charge body to aidhand positioning the device at the target.

The liner material may take any convenient form which can produce ashaped charge liner collapse mechanism, the so-called “Munroe effect”,and typically include conical liner configurations and hemispherical andhemispherical cap geometries.

A method of triggering an avalanche according to the present inventioncomprises positioning an explosive device or explosive device assemblyof the present invention in a predetermined position relative to a snowor ice formation and detonating said explosive device or deviceassembly.

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings of which:

FIG. 1 is a diagrammatic sectional view of a first device according tothe present invention;

FIG. 2 is a diagrammatic sectional view of a second device according tothe present invention;

FIGS. 3, 4 and 5 are diagrammatic views of the results of recentexperimental cratering trials conducted against level and stable snowpack;

FIGS. 6 to 8 are diagrammatic views of the use of an explosive devicewhich is as the device of FIG. 1 but with a support stick affixed to it;

FIG. 9 is a diagrammatic view of a further embodiment of the presentinvention for cornice control;

FIG. 10 is a further diagrammatical sectional view of a furtherembodiment of an assembly comprising two devices of FIG. 1;

FIG. 11 is a diagrammatic view of a typical application of the device ofFIG. 10 for avalanche control;

FIG. 12 is a diagrammatic sectional view of a further embodiment of anassembly comprising two devices of FIG. 1;

FIG. 13 is a diagrammatic view of a typical application for the deviceof FIG. 12 for avalanche control;

FIG. 14 is a diagrammatic sectional view of a further embodiment of theinvention within the body of a modified Avalauncher gas gun round;

FIG. 15 is a diagrammatic sectional view of a further application of theexplosive charge assembly of FIG. 14; and

FIG. 16 is a diagrammatic sectional view of a further embodiment of thepresent invention.

Referring to FIG. 1, an explosive device 10 consists of a cylindricalGRP (glass reinforced plastic) body 2 located between a PERSPEX magazinelocating plate 4 and PERSPEX liner locating plate 6. The magazinelocating plate 4 centralises a PERSPEX unit 8 on the central axis of thedevice. The magazine unit 8 locates a detonator 12 and explosive boosterpellet 14 to form an initiation cap assembly 16. The initiation capassembly 16 ensures that the detonation front transferred into a mainexplosive filling 18, via the booster pellet 14, is propagatedsymmetrically with respect to the axis of the device 10. A GRP outerliner skin 22, with an open truncated apex 24 is bonded to thecylindrical body 2 to form a sub-assembly 26. An internal GRP conicalliner 32, with a closed truncated apex, is bonded into the recess 34machined into the liner locating plate 6 to form a sub-assembly 36.Sub-assemblies 26 and 36 are then joined and bonded to form a chargeassembly 42 defining a conical void 44 concentric and aligned to thecentral axis of the device 10.

The material and grist size of a particulate liner cavity filling 45 ischosen to suit the nature of the target material involved. For avalanchecontrol work, aluminium powder of 150 micron particle size is suitable,for example. The filling 45 is loaded into the void 44 through a fillingport 24 at the apex of the liner 22. The filling port is then sealedwith a disk of aluminium adhesive tape 46. The explosive filling 18 isthen loaded into the charge assembly 42 and the charge is closed byfitting and bonding the initiation cap 16 in place. A hole 48 in theliner locator plate 6 allows pressure equalisation between the conicalvoid enclosed by the inner liner skin 32 and liner locator plate 6 andexternal atmospheric pressure and has no other bearing on the functionof the vice.

Referring now to FIG. 2, a device 20 consists of a cylindrical body 50located between an initiation cap 16 and a PERSPEX tubular linerassembly locator plate 35. The initiation cap 16 ensures that thedetonation front is transferred into a radial detonation transfer disk51, symmetrically disposed with respect to the axis of the device 20. Aninner GRP tubular liner 52 and outer GRP tubular liner 53 are locatedco-axially between a polyethylene barrier plate 59 and the tubular linerassembly locator plate 35. The separation between the two tubular liners52 and 53 is maintained by in insert 54 which is drilled with a singlehole 55 to allow a void 56 defined by the liners 52 and 53 to be filledwith aluminium powder 58.

The barrier plate 59, inner and outer tubular liners, 52 and 53respectively, and insert 54 are bonded together to form a tubular linerassembly 57, The void 56 between the inner and outer tubular liners isfilled with aluminium powder 58, of 150 micron particle size, throughthe filling hole 55 which is then sealed with a disk of aluminiumadhesive tape, (not shown). The radial detonation transfer disk 51 isbonded to the inner face 58 of the initiation cap assembly 16 and thebarrier plate 59 of the tubular liner assembly 57 is bondedconcentrically to the outer face 62 of the radial detonation transferdisk 51. A main explosive filling 64 is filled into the charge assemblyfrom the open end opposite the initiation cap 16 and closed and sealedby fitting and bonding the tube locator plate 34 in position.

FIGS. 3, 4 & 5 show the results of experimental cratering trials of theexplosive device of FIG. 1 conducted against a level and stable snowpack 66. Each charge was set 1.2 m below the snow surface such that itsaxis was horizontal and the point of detonation 68 arranged such thatany bias would be driven in the direction of the arrow. After firing,the craters were sectioned to reveal the profiles shown in the figures.The depth of the snow base is indicated by a solid black line 72

The profile 74 shown in FIG. 3 was produced by a 1 kg blast explosivecharge 70. The charge was 68 fired to establish a control standardagainst which the experimental charge firings of devices according tothe present invention could be compared. The profile was symmetricalabout the vertical axis and yielded a crater volume of 2.7 cubic meters.

The profile 76 shown in FIG. 4 was produced by the device 10 describedearlier and shown in FIG. 1. The explosive content was also 1 kg. Theeffects of the conical liner are clear. The crater was elongated as aresult of the penetration and subsequent secondary reaction of theshaped charge jet. A significant increase in the energy transmissioninto the snow pack was evident, the crater volume increasing from 2.7 to11.9 cubic meters.

The profile 78 shown in FIG. 5 was produced by the device 20 describedearlier and shown in FIG. 2. The explosive content was also 1 kg. Thisliner configuration produced more localised reaction of the linermaterial. The crater volume was increased from 2.7 to 7.8 cubic meters.This was less than that produced by the conical liner configuration. ofdevice 10 but particularly high shock emission was evident from theground shock detected and extensive secondary surface spalling at theinner surface of the crater.

There will now be described exemplary applications of the device 10 ofFIG. 1. It should be note that the applications are equally valid forthe device 20 of FIG. 2 and liner geometries that fall between the two,the choice being made to suit the characteristics of the particulateloading material, operational environment, cost, and target mediuminvolved.

FIGS. 6 to 8 illustrate the use of an explosive device 40 which is asdevice 10 of FIG. 1 but with a support stick 82 affixed to it so thedevice can be positioned and orientated as required on a snow slab. Thedevice 40 includes a pyrotechnic fuze 88. The highly focused blastemission produced by the enhanced blast charge 10 is indicatedschematically by the extended, highly schematic “star” shaped blastenvelope 84. They respectively illustrate the use of the device forcornice overhang removal with the device 40 providing combined air shockand deep penetration, slab blasting with the device providing combinedair shock and deep penetration perpendicular to the snow slab, and slabblasting where the device is orientated to provide superficialdisruption of the surface layer of a snow slab.

FIG. 9 shows a further use of the present invention for cornice control.The device 50 is as the device 10 of FIG. 1 but includes a pyrotechnicfuze 88 and a conical end cap 86 to aid penetration into the soft backof the cornice following remote delivery of the device from a shortrange launcher system, typically a cross bow.

FIG. 10 shows a further embodiment of the present invention, namely anassembly 60 comprising two devices 10 of FIG. 1, located back to backwithin a thin cardboard tube 92. A smaller diameter cardboard tube 94,located inside the main tube 92, holds the devices apart and tape 96 ateach end retains the two devices 10 in place. Each device 10 isconnected to an identical length of shock tube 98 (Dyno-Nobel StarterLine), terminated at the charge end by an instantaneous standarddetonator cap 102. The starter lines 98 pass out of the locating tubes92 and 94 via hole 104 and are fixed securely to the outer tube 92 byadhesive tapes 106.

The assembly 60 of FIG. 10 produces a simultaneous detonation of thecharges 10 which project a highly focused axi-symmetric blast wavetravelling in opposite directions along the axis of the assembly asindicated by the blast envelope 99.

FIG. 11 shows a typical application for the device 60 of FIG. 10 foravalanche control. The assembly 60 is arranged to overhang a cornicebuild up such that the axis of the charge is parallel to the line of thecornice. The two starter lines 98 are initiated simultaneously from afiring point 70 in known manner.

FIG. 12 shows a further embodiment of the present invention, namely anassembly 80 comprising two devices 10 of FIG. 1, located face to facewithin a thin cardboard tube 108. A smaller diameter cardboard tube 112,located inside the main tube 108, establishes a separation between thecharges 10 that can be changed in length to alter the output of thecharge assembly. The charges 10 are retained in the outer tube 108 byadhesive tape as described for FIG. 10. Each device 10 is connected toan identical length of shock tube 114 (Dyno-Nobel Starter Line),terminated at the charge end by an instantaneous standard detonator cap116. The two starter lines are then crossed over the outer tube 108 andtaped securely as described for FIG. 10.

The assembly 80 of FIG. 12 produces simultaneous detonation of thecharges. When the jets formed by the two shaped charge liners collide,in accordance with simple principles of momentum balance, a symmetrical360 degree disk of high pressure products 109 is emitted in a plane at90 degrees to the axis of the two charges.

FIG. 13 shows a typical application for the device of FIG. 12 foravalanche control. The assembly 60 is arranged to overhang a cornicebuild up such that the axis of the charge is parallel to the line of thecornice. The two starter lines 98 are initiated simultaneously from thefiring point 70. This arrangement may be equally effective if suspendedsuch that the axis of the assembly 80 runs vertically.

FIG. 14 shows an embodiment 90 of the current invention within the bodyof a modified Avalauncher gas gun round 90. An assembly 125 consists ofa plastics nose cone 118, a full calibre body shell 119, containing theexplosive filling 122, and an enhanced blast shaped charge linerassembly 123, as described for device 10 of FIG. 1, and a plastics tailfin adaptor 124 of known form. The explosive charge assembly 125 isstored separately from a known tail fin assembly 126, which embodies thesafety and arming mechanism (not detailed) and detonator 128. Thisconfiguration significantly improves the performance of the standardAvalauncher blast round as shown in FIGS. 3 and 4, respectively.

FIG. 15 shows a further embodiment 100 employing the above explosivecharge assembly 125 but this time in conjunction with the shock tubefiring and control system described in detail filed in copending BritishPatent Application No 9915586.3 the entire contents of which areincorporated by reference into this application. This embodiment 100 isa cost effective engineering solution, for application of theexperimental configurations described in FIGS. 1 and 2, to hand chargeavalanche control operations. Briefly, the free end 132 of a Dyno-Nobelstarter line is attached to the operator (not shown). The remainder ofthe starter line is coiled as a coil 134 within a cardboard spool tube136, eventually terminating at a detonator end 138 forming a spoolassembly 142 which is retained 144 on the body of the Avalauncherexplosive charge assembly 125 by adhesive tape 144. The charge assembly100 may be thrown or launched to the desired position, the first end 132of the starter line being subsequently detached from the operator andconnected to a firing pack (not shown) ready for firing.

Referring now to FIG. 16, this embodiment of the present invention is around 150 having a body 152 and nacelle 154, both of injection mouldedpolypropylene, joined together by a joint ferrule 156, also ofpolypropylene, held together by pairs of male/female clip rings (notshown) moulded into the three components 152, 154, 156.

The body 152 is tapered to minimise aerodynamic drag and has thenecessary base features to interface with previous described aerodynamicfin 126 and firing assembly of FIG. 14.

The nacelle also provides aerodynamic streamlining and a stand offbetween the mouth of a shaped charge liner 158 and target material (notshown). Alternative nacelle shapes could be employed to control thedetonation delay time in soft snow pack, for example.

The joint ferrule 156 also retains the liner 158 and a series of HEpellets HE₁ to HE₆ within the body component. Note that there is a 1 mmclearance gap between the liner 158 and joint ferrule 156 to accept asoft packing washer 160 to control thermal effects and tolerancebuild-up.

The liner 158 is pressed from aluminium powder bound with paraffin wax,this allows a broad range of different liner compositions to beintroduced to adjust performance to suit varying conditions and/oralternative applications. A range of different liner geometries can alsobe used for the HE₁ pellet. The liner 158 of this embodiment has adensity of 1.7 g/cc.

The explosive charge consists of a set of pre-pressed pellets HE₁ toHE₆. This construction allows a range of different explosivecompositions to be introduced to adjust performance to suit varyingconditions and/or alternative applications. Typically, aluminisedexplosive (addition of up to 20% of Al. powder) significantly enhancesblast yield from pellets HE₃, HE₄, HE₅ and HE₆, but pellets HE₁ and HE₂could be a high density HMX and/or RDX/wax composition, more ideallysuited to the shaped charge function. However, all pellets (HE₁ to HE₆)could be aluminised to optimise blast yield.

A wave shaping barrier 162 (injection moulded polypropylene) shapes thegeometry of the detonation from and influences the way in which theshaped charge liner collapses. A broad range of different effects can beboth introduced and controlled by altering the shape of the barrier 162.The introduction of a separate pellet that accommodates the barrierfeature pellet HE₂ allows for such changes to be made at will.

The nacelle 154 has a bead 168 round the inside of the nacelle 154tapered rearwardly to permit a bowed plenum 166 to be pushed forwardlyover the bead 168 and held in position inside the nacelle 154.

The front most region of the interior volume of the nacelle 154 isfilled with aluminium powder 164 and held in place by the plenum 166 butother materials can be placed there, eg aluminised paraffin wax.

A throughhole 172 in the nacelle 154 allows the injection of a lowdensity filler, eg polyurethane foam, about 0.01 gm/cm², to fill thevolume 170 which is in the collapse zone forward of the liner 158. Thisadds rigidity to the forward structure of the device and providessupport to the liner 158 so permitting the use of more frangible linersthan otherwise possible.

The material 164 in the nacelle 154, if present, is energised, dispersedand propelled forward by the jet formed on detonating the device, toreact with either the target material and/or the atmosphere ahead of thenacelle.

An alternative embodiment of the device of FIG. 16 is one in which thereis no particulate material 164. In a further embodiment, the liner 158may be omitted, with suitable dimension changes of the pellet HE₁ toaccommodate the gap that would otherwise be present between it and thewasher 160 or replaced by a liner not having any dispersible material inits composition. Such an embodiment would be applied where minimalpenetration effects were required, typically, the production of a highlydirectional gaseous blast effect. The magnitude of the focused blasteffect could be further enhanced by causing the gaseous jet formed bythe cavity in the explosive to interact with a particulate or reactivematerial 164 contained within the nacelle.

Although the use of present invention has been described in terms ofavalanche control applications, the benefits of controlled and highlydirectional cutting, perforation or stimulation of secondary reactionsof explosive devices according to the present invention has a wide rangeof other potential applications. These include:

rapid generation of wide access holes in concrete/rock walls in supportof rescue and recovery operations, where a range of liner materials andparticle sizes for the liner can be chosen to control the nature of thecut and/or residual particle penetration into sensitive areas behind;

the use of directing the highly focused blast effects to combat andextinguishing burning oil wells;

rapid internal cutting of narrow bore, thick walled pipes, typical ofwell liners and drilling shafts; and

spalling of loose rock from chamber roofs in underground mines, civiltunnelling and mining operations and underwater engineering operations.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method of blasting a snow or ice formationtarget including a given material comprising, (a) providing a hollowcharge explosive device including an explosive charge defining at leastone boundary wall of a cavity and including particulate material locatedforward of said boundary wall so as to be dispersible by said explosivecharge when detonated, said particulate material being selected to beone which reacts with water on detonation of the explosive device, (b)positioning said explosive device in a predetermined position relativeto the snow or ice formation target, and (c) detonating said explosivedevice thereby triggering an avalanche.
 2. A method as claimed in claim1, in which said explosive device is positioned by launching saidexplosive device by hand or by mechanical or chemical propulsion.
 3. Amethod as claimed in claim 1, wherein said particulate material isincluded in a liner, said liner lining said cavity.
 4. A method asclaimed in claim 3, in which said liner comprises an inner liner skinand an outer liner skin spaced apart from said inner line skin, and saidparticulate material is a loose powder located between said inner linerskin and said outer liner skin.
 5. A method as claimed in claim 4,wherein said inner liner skin and said outer liner skin are formed froma glass reinforced plastics material.
 6. A method as claimed in claim 1,in which said particulate material is embedded in a solid binder.
 7. Amethod as claimed in claim 1, in which said particulate material hasbeen consolidated by mechanical pressure.
 8. A method as claimed inclaim 1, in which said particulate material is aluminum powder.
 9. Amethod as claimed in claim 1, in which said particulate material reactswith a predetermined target medium.
 10. A method as claimed in claim 1,further comprising a nacelle forward of said cavity, and wherein saidparticulate material is located in said nacelle.
 11. A method as claimedin claim 1, wherein said device is embodied in a gun firable or handthrowable, or mechanically or chemically launchable projectile.
 12. Amethod as claimed in claim 1, wherein said device includes a liner whichliner includes aluminum powder bound by wax.
 13. A method as claimed inclaim 12, wherein said wax is paraffin wax.
 14. A method as claimed inclaim 1, wherein said explosive charge includes two or more highexplosive pellets.
 15. A method as claimed in claim 14, wherein one ormore of the high explosive pellets is aluminized.